Autochthonous dengue fever in Croatia, AugustSeptember 2010

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E u r o p e ’ s l e a d i n g j o u r n a l o n i n f e c t i o u s d i s e a s e e p i d e m i o l o g y, p r e v e n t i o n a n d c o n t r o l

Rapid communications

Autochthonous dengue fever in Croatia, August–September 2010 2 by I Gjenero-Margan, B Aleraj, D Krajcar, V Lesnikar, A Klobučar, I Pem-Novosel, S Kurečić-Filipović, S Komparak, R Martić, S Đuričić, L Betica-Radić, J Okmadžić, T Vilibić-Čavlek, A Babić-Erceg, B Turković, T Avšić-Županc, I Radić, M Ljubić, K Šarac, N Benić, G Mlinarić-Galinović

Evolution of the haemagglutinin gene of the influenza A(H1N1)2009 virus isolated in Hong Kong, 2009–2011 6 by GC Mak, CK Leung, KC Cheng, KY Wong, W Lim

Surveillance and outbreak reports

Hepatitis A outbreak predominantly affecting men who have sex with men in Northern Ireland, October 2008 to July 2009 11by O Sfetcu, N Irvine, SL Ngui, C Emerson, C McCaughey, P Donaghy

Perspectives

Evaluation of syndromic surveillance in the Netherlands: its added value and recommendations for implementation 17by CC van den Wijngaard, W van Pelt, NJ Nagelkerke, M Kretzschmar, MP Koopmans

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Autochthonous dengue fever in Croatia, August–September 2010

I Gjenero-Margan ([email protected])1, B Aleraj1, D Krajcar2, V Lesnikar2, A Klobučar2, I Pem-Novosel1, S Kurečić-Filipović1, S Komparak3, R Martić3, S Đuričić4, L Betica-Radić4, J Okmadžić5, T Vilibić-Čavlek1, A Babić-Erceg1, B Turković1, T Avšić-Županc6,I Radić1, M Ljubić7, K Šarac1, N Benić2, G Mlinarić-Galinović1

1. Croatian National Institute of Public Health, Zagreb, Croatia2. Public Health Institute of the City of Zagreb ‘Dr. A. Štampar’, Zagreb, Croatia3. Dubrovnik–Neretva County Public Health Institute, field unit Korčula/Pelješac, Korčula, Croatia4. Dubrovnik County Hospital, Infectology ward, Dubrovnik, Croatia5. Primary Health Care Unit Orebić, Orebić, Croatia6. Institute for Microbiology and Immunology, Medical faculty, Ljubljana, Slovenia7. Public Health Institute of Dubrovnik Neretva County, Epidemiology service, Dubrovnik, Croatia

Citation style for this article: Gjenero-Margan I, Aleraj B, Krajcar D, Lesnikar V, Klobučar A, Pem-Novosel I, Kurečić-Filipović S, Komparak S, Martić R, Đuričić S, Betica-Radić L, Okmadžić J, Vilibić-Čavlek T, Babić-Erceg A, Turković B, Avšić-Županc T, Radić I, Ljubić M, Šarac K, Benić N, Mlinarić-Galinović G. Autochthonous dengue fever in Croatia, August–September 2010. Euro Surveill. 2011;16(9):pii=19805. Available online: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19805

Article published on 3 March 2011

After information about a dengue case in Germany acquired in Croatia, health professionals and the pub-lic in Croatia were alerted to assess the situation and to enhance mosquito control, resulting in the diagno-sis of a second case of autochthonous dengue fever in the same area and the detection of 15 persons with evidence of recent dengue infection. Mosquito control measures were introduced. The circumstances of den-gue virus introduction to Croatia remain unresolved.

IntroductionThe epidemiology service of the Croatian National Institute of Public Health (CNIPH) has registered six imported cases of dengue virus (DENV) infection since 2007. All except one were Croatian citizens who had spent time in areas with local transmission of this dis-ease (Southeast Asia, South America) and had a mild clinical presentation of dengue fever. The sixth case occurred in 2007 in a tourist visiting Croatia who devel-oped haemorrhagic fever and had previously travelled in South-east Asia [1,2]. Although a seroepidemiology study conducted in 1980 in a limited area of north-eastern Croatia in healthy young inhabitants proved the presence of antibodies to DENV type 2 (3,9%) and type 1 (2,1%) [3], no cases of dengue fever were regis-tered by the health services.

Aedes albopictus was for the first time recorded in Croatia in 2004 in the area surrounding Zagreb [4]. Within two years, Ae. albopictus was found on the entire territory of the Adriatic coast from northern Istria to Dubrovnik in the south. According to routine monitoring of mosquitoes and published articles, Ae. albopictus is now permanently established in the coastal but not yet in the continental areas of Croatia [5].

Soon after reports on the first autochthonous DENV infection diagnosed in France in September 2010 [6], the Epidemiology Service of the CNIPH was notified on 30 September by the Robert Koch Institute (RKI) in Germany of a German citizen, who fell ill with symp-toms of dengue fever immediately after returning to Germany from a 15-day stay on the Pelješac peninsula in Croatia. Virological investigation revealed the pres-ence of DENV-specific IgM, a rise in DENV-specific IgG and the presence of NENV NS1 antigen in the patient’s blood [7]. As this was the first case of dengue fever probably acquired in Croatia, an epidemiological inves-tigation was conducted and outbreak control measures implemented. We present here the first results of the epidemiological investigation.

Active case findingAccording to information received by the RKI, the German citizen travelled from Germany via Austria and Slovenia along the Croatian coast in August 2010 and stayed on the Pelješac peninsula and the island of Korčula for 15 days. The disease onset was on the day after he returned to Germany. The information received from RKI on the first autochthonous case of dengue fever was sent to the World Health Organization (WHO) via the International Health Regulations (IHR) informa-tion network [8] by the national IHR focal point (the epidemiology service of the CNIPH) and disseminated to the Croatian and international public via the media in order to increase local and international awareness.

The epidemiological investigation started in Pelješac and Korčula, and will be gradually expanded to the entire Croatian littoral. The CNIPH released a circula-tory letter informing all epidemiology services and hospital infectology clinics in the country to consider the possibility of dengue fever in clinically compat-ible cases including those with no history of travelling

3www.eurosurveillance.org

abroad. The circulatory letter contained the entire range of clinical manifestations of dengue fever, and for the purposes of the epidemiological investigation, a question on diseases accompanied with fever occur-ring in the village where the German tourist had stayed. At the time of the first epidemiological investigation among local physicians in the beginning of October 2010, there were no such acute diseases in the area. In the following weeks, a number of clinically suspect cases were reported and serum samples were sent to the CNIPH, but tested negative for dengue virus (Anti-Dengue virus Elisa IgM/IgG, Euroimmun, Germany).

On 22 October 2010, a possible case of dengue fever was reported in a resident of the same village where the German patient had stayed. The Croatian patient, a woman in her fifties, who had not travelled outside her place of residence, developed symptoms compatible with dengue fever on 17 October, including temperature up to 39°C, skin rash, chill, headache and joint and muscle pain, and was admitted to the infectology ward at Dubrovnik hospital on day 6 after onset of disease.

Laboratory diagnosisA serum sample was taken from the Croatian patient on admission to hospital and sent to the National Reference Laboratory for Arboviral Infections at the Virology department of the CNIPH in Zagreb. Virological analysis by ELISA (Anti-Dengue virus ELISA IgM/IgG Euroimmun, Germany) detected DENV-specific IgM (ratio 1.9). The sample was negative for DENV-specific IgG (10 relative units (RU)/ml), West Nile virus (WNV) IgM and IgG (Anti-West Nile virus ELISA IgM/IgG, Euroimmun, Germany), and chikungunya virus IgM and IgG. (Anti-Chikungunya virus ELISA, IgM/IgG, Euroimmun, Germany).The patient had not been vac-cinated against yellow fever or tick-borne encephalitis (TBE). The village of residence as well as whole south-ern Croatia is not endemic for TBE [9]. Considering the current epidemiological situation in Croatia these labo-ratory results pointed to a diagnosis of dengue fever [10].

The patient’s first serum was also sent to the regional reference laboratory in Ljubljana (Slovenia) where an RT-PCR was negative for dengue virus [11]. The second (paired) serum was taken on day 19 after onset of ill-ness when the patient was already discharged and recovered, and the sample was analysed at CNIPH with the following results: DENV: IgM-positive (ratio 4.9) and IgG-positive (110 RU/ml); WNV: IgM-positive (ratio 1.2) and IgG-negative; and chikungunya virus: IgM- and IgG-negative. These results confirmed this case as the second autochthonous case of dengue fever in Croatia.

Analysis of serum samples collected in the areaWe collected 14 blood samples from healthy inhab-itants living near the case’s place of residence. The samples were analysed by ELISA for the presence of DENV and WNV IgM/IgG antibodies. Nine of those were

found positive for DENV infection (IgG) and seven had positive or borderline results for DENV-specific IgM (Table 1).

A further 112 sera collected from anonymous patients who had sought medical care from various reasons during October 2010 were available at the laboratory of the local health centre. These sera were tested at

Table 3Adult mosquitoes caught in Podobuče, Orebić and Korčula, Croatia, October 2010

Species NumberAedes albopictus 49Ochlerotatus mariae 4Ochlerotatus sp. 2Culex pipiens 5Culiseta annulata 1Total 61

Table 2Distribution of antibodies to dengue virus in six anonymous serum samples, Croatia, October 2010

Examinee number 1 2 3 4 5 6

DENV IgM (ratio)a +/- (0.9)

+/- (0.8)

+/- (1.08)

+ (4.6)

+ (2.2) -

DENV IgG (RU/ml)b + (72)

+ (46)

+ (40)

+ (46)

+/- (<2)

+ (153)

DENV: dengue virus.a <0.8 negative (-), 0.8-1.1 borderline (+/-), ≥ 1.1 positive (+). Results are expressed as ratio according to the manufacturer’s specifications.b <16 negative (-), 16-22 borderline (+/-), ≥ 22 positive (+). Results are expressed in RU/ml according to the manufacturer’s specifications.

Table 1Distribution of antibodies to dengue virus in nine persons from a pool of 14 neighbours of the autochthonous case from Pelješac, Croatia, October 2010

Examinee numberDENV IgM

(ratio) a DENV IgG (RU/ml) b

1 + (2.4) + (155)2 +/- (1.04) + (126)3 + (2.2) + (98)4 + (1.2) + (140)5 - (0.3) + (170)6 - (0.5) + (155)7 + (2.3) + (138)8 + (2.4) + (94)9 + (2.6) + (170)

DENV: dengue virus.a <0.8negative (-), 0.8-1.1 borderline (+/-), ≥1.1 positive (+). Results are expressed as ratio according to the manufacturer’s specifications.b <16 negative (-), 16-22 borderline (+/-), ≥22 positive (+). Results are expressed in RU/ml according to the manufacturer’s specifications.


CNIPH for the presence of DENV and WNV antibodies. Ethics approval was not required and informed con-sent was not sought. The work was carried out under the Communicable Disease Protection and Control Act which provides statutory support for investigations conducted for the purpose of communicable disease control.

Of those 112 samples, six were positive for DENV-specific antibodies. In all six positive sera, DENV-specific IgG was found (one sample with a borderline value). DENV-specific IgM were found in five sera: clearly positive in two and borderline in three (Table 2). All 112 sera were negative for WNV IgM and IgG.

Entomological investigation During the field investigation the presence of mos-quitoes was noticed, despite mandatory disinsec-tion implemented on the entire Croatian territory. Mosquitoes were caught in the place of probable trans-mission and also on the island of Korčula in October 2011 with the aim of identifying the mosquito species present and determining whether they were carrying DENV. Two days after the mosquito had been caught, adulticidal and larvicidal disinsection was conducted at the village where the German patient had stayed.

The 61 caught mosquitoes were identified by an ento-mologist (Table 3). The species Ae. albopictus domi-nated (49 of 61).

Virological investigation was conducted for 44 Ae. albopictus adults in eight pools containing between five and seven mosquitoes. All eight pools tested neg-ative for DENV in the RT-PCR conducted at the WHO Regional Reference Laboratory for Arboviruses at the Institute for Microbiology and Immunology in Ljubljana, Slovenia [11].

DiscussionAfter France, Croatia is the second country in Europe in which autochthonous transmission of dengue infec-tion has been shown, which had not been recorded in Europe since the epidemic in Greece in 1925 to 1928 [12-15]. According to data of the communicable dis-ease epidemiology service of the CNIPH, registered imported cases of dengue are not frequent (six cases in three years). Although until recently dengue fever was not a notifiable disease in Croatia, it is unlikely that the epidemiology service network which collabo-rates with the laboratories that conduct the diagnosis would have missed the occurrence of a confirmed case of imported dengue fever.

The assumption that the German tourist acquired den-gue fever in the region of the Pelješac peninsula was confirmed by the identification of a second case of den-gue fever in a local citizen who had not travelled out-side the area. Although the antigen was not confirmed by RT-PCR in the acute serum of the patient, taken six days after illness onset, the presence of specific IgM

antibodies (IgG was negative) pointed to acute infec-tion. This was confirmed in a sample taken on day 19 of the illness when IgM and IgG antibodies were found.

Nine of the 14 samples taken from the Croatian patient’s neighbours, none of whom had travelled out-side Croatia, were IgG-positive, and we assume that these were relatively recent infections because seven of them were also IgM-positive. Some of them reported having an influenza-like disease in August and early September. Moreover, DENV-specific antibodies were found in 5.4% of the anonymous serum samples col-lected in October 2010 by the laboratory that covers the area of Pelješac and Korčula. Five of the six DENV-positive sera in this panel showed borderline or posi-tive values of IgM antibodies against DENV. Based on the available serological and epidemiological data we therefore assume that a cluster of acute DENV infection occurred in the area, most probably during August and September 2010.

Each cluster of infectious diseases is reported using the national communicable diseases early warn-ing system. During summer 2010 there were no such reports from Pelješac. Only four of the DENV-positive villagers contacted health services for febrile illness in August and September and were not recognised as an outbreak. At that time of year, there is an increased circulation of enteroviruses which can manifest with similar symptoms, but we believe that the main reason why dengue fever was not suspected in these patients is the fact that this illness had not been registered in Croatia or Europe so far and is therefore not consid-ered in persons who have no travel history to endemic areas. Although the health services had been alerted of the possibility of new diseases transmitted by Ae. albopictus, particularly following the chikungunya fever outbreak in Italy in 2007 [16], it was only after our circulatory letter in October that dengue virus infection in local inhabitants was suspected by general prac-titioners and subsequently confirmed in the second autochthonous Croatian case described in this paper. There may also have been other dengue virus infec-tions with an inapparent or mild course. We believe that other tourists staying in the area may have returned to their home countries with dengue fever, but there have been no reports of exported cases other than the German case.

It is likely that the dengue virus was imported into this community during the summer months of 2010. Regarding the manner of importation, we can only speculate. It could have been through infected travel-lers arriving from endemic areas in whom the infection was not recognised. Bearing in mind that Ae. albopic-tus species have spread along the Adriatic coast, also in the region of Pelješac and Korčula mainly through transport by sea [5], importation of infected mosqui-toes in the same manner cannot be excluded. Since the role of transovarial transmission in mosquitoes is questionable [17,18], it is not likely that importation


happened through infected eggs or larvae (e.g. in used car tires).

Croatia will continue to alert health practitioners to the presence of this disease. Larvicidal and adulti-cidal mosquito control measures already applied in the affected area will be continued and expanded to the entire country to prevent further establishment of den-gue fever or other diseases transmitted by the same vector, such as chikungunya fever [19,20]. Selection of blood donors in the country is in line with all interna-tionally accepted criteria, in that any febrile illness in a potential donor presents a contraindication including the period of convalescence. This covers dengue virus infections well, as cases are only infective during the febrile phase and there is no chronic infection stage. A short prodromal period can pose a risk, but the regular delayed use of blood donations allows to investigate all donors who fall ill in the first two days after dona-tion and to discard their blood if necessary. However, the possibility of transient asymptomatic dengue virae-mia needs to be taken into account in practice if the disease were to become established.

References1. Croatian National Institute of Public Health. Imported dengue.

Epidemiological news. August 2007;8. Available from: http://www.hzjz.hr/epidemiology/news/index0708.htm

2. Pinazo MJ, Munoz J, Betica L, Maretic T, Zekan S, T Avsic-Zupanc, et al. Imported dengue hemorrhagic fever, Europe. Emerg Infect Dis. 2008;14(8):1329-30.

3. Ropac D, Gould E, Punda V, Vesenjak-Hirjan J. [Dengue viruses in northeastern Croatia]. Lijec Vjesn. 1988;110(6-7):177-80. Croatian.

4. Klobucar A, Merdic E, Benic N, Baklaic Z, Krcmar S. First record of Aedes albopictus in Croatia. J Am Mosq Control Assoc. 2006;22(1):147-8.

5. Klobucar A, Benic N. Azijski tigar komarac, Stegomyia albopicta (Aedes albopictus) u Zagrebu i Hrvatskoj [The Asian Tiger Mosquito Stegomyia albopicta (Aedes albopictus) in the City of Zagreb and Croatia]. HCJZ2006;2(8) Available from: http://www.hcjz.hr/clanak.php?id=13022

6. La Ruche G, Souarès Y, Armengaud A, Peloux-Petiot F, Delaunay P, Desprès P, et al. First two autochthonous dengue virus infections in metropolitan France, September 2010. Euro Surveill. 2010;15(39):pii=19676. Available from: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19676

7. Schmidt-Chanasit J, Haditsch M, Schöneberg I, Günther S, Stark K, Frank C. Dengue virus infection in a traveller returning from Croatia to Germany. Euro Surveill. 2010;15(40):pii=19677. Available from: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19677

8. World Health Organization (WHO). International health regulations (IHR) 2005. Second edition. Geneva:WHO; 2008. Available from: http://www.who.int/ihr/en

9. Borcic B, Kaic B, Kralj V. Some epidemiological data on TBE and Lyme borreliosis in Croatia. Zentralbl Bakteriol. 1999;289(5-7):540-7.

10. Wichmann O, Stark K, Shu PY, Niedrig M, Frank C, Huang JH, et al. Clinical features and pitfalls in the laboratory diagnosis of dengue in travelers. BMC Infect Dis. 2006;6:20.

11. Leparc-Goffart I, Baragatti M, Temmam S, Tuiskunen A, Moureau G, Charrel R, de Lamballerie X. Development and validation of real-time one-step reverse transcription-PCR for the detection and tayping of dengue viruses. Journal of Clinical Virology 45 (2009) 61-66.

12. World Health Organization (WHO). Global Alert and Response. Impact of dengue. Geneva: WHO. [Accessed 27 Sep 2010]. Available from: http://www.who.int/csr/disease/dengue/impact/en/index.html

13. Jelinek T. Trends in the epidemiology of dengue fever and their relevance for importation to Europe. Euro Surveill. 2009;14(25):pii=19250. Available from: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19250

14. Papaevangelou G, Halstead SB. Infections with two dengue viruses in Greece in the 20th century. Did dengue hemorrhagic fever occur in the 1928 epidemic? J Trop Med Hyg. 1977;80(3):46-51.

15. Rosen L. Dengue in Greece in 1927 and 1928 and the pathogenesis of dengue hemorrhagic fever: new data and a different conclusion. Am J Trop Med Hyg. 1986;35(3):642-53.

16. Angelini R, Finarelli AC, Angelini P, Po C, Petropulacos K, Macini P, et al. An outbreak of chikungunya fever in the province of Ravenna, Italy. Euro Surveill. 2007;12(36):pii=3260. Available from: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=3260

17. Lee HL, Rohani A. Transovarial transmission of dengue virus in Aedes aegypti and Aedes albopictus in relation to dengue outbreak in an urban area in Malaysia. Dengue Bulletin 2005;29:106-11. Available from: http://www.searo.who.int/LinkFiles/Dengue_Bulletins_Volumes_29_(2005)_CHAPTER13.pdf

18. World Health Organization (WHO). Dengue Gudelines for Diagnosis, Treatment, Prevention and Control. New edition 2009. Geneva:WHO. Available from: http://whqlibdoc.who.int/publications/2009/9789241547871_eng.pdf

19. Croatian National Institute of Public Health. Activities to maintain current low density of populations of Aedes albopictus in Croatia. Epidemiological news. July 2008:7. Available from: http://www.hzjz.hr/epidemiology/news/index0807.htm

20. Scholte EJ, Braks MAH. Mosquito surveillance methods implemented in Europe. European Centre for Disease Prevention and Control (ECDC). 31 January 2010. Available from: http://www.ecdc.europa.eu/en/activities/sciadvice/Lists/ECDC%20Reviews/ECDC_DispForm.aspx?List=512ff74f%2D77d4%2D4ad8%2Db6d6%2Dbf0f23083f30&ID=760&RootFolder=%2Fen%2Factivities%2Fsciadvice%2FLists%2FECDC%20Reviews



Evolution of the haemagglutinin gene of the influenza A(H1N1)2009 virus isolated in Hong Kong, 2009–2011

G C Mak1, C K Leung1, K C Cheng1, K Y Wong1, W Lim ([email protected])1

1. Virology Division, Public Health Laboratory Services Branch, Centre for Health Protection, Department of Health, Kowloon, Hong Kong

Citation style for this article: Mak GC, Leung CK, Cheng KC, Wong KY, Lim W. Evolution of the haemagglutinin gene of the influenza A(H1N1)2009 virus isolated in Hong Kong, 2009–2011. Euro Surveill. 2011;16(9):pii=19807. Available online: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19807


Phylogenetic analysis of the haemagglutinin (HA) gene shows that the influenza A(H1N1)2009 viruses col-lected in Hong Kong clustered in two main branches characterised by the E391E and E391K amino acids. The main branch E391K evolved in two sub-branches with N142D and S202T mutations that first appeared in March and July 2010, respectively, with the lat-ter becoming the predominant strain. These genetic variants that emerged display similar antigenic char-acteristics. Concurrent with genetic surveillance, lab-oratories should continue monitoring the circulating viruses antigenically.

IntroductionInfluenza A(H1N1)2009 virus is a reassortant of swine, avian and human influenza viruses which is antigeni-cally different from seasonal influenza A(H1N1) viruses circulating previously [1]. In Hong Kong, the first case was detected in a visitor from Mexico on 1 May 2009. The infection spread locally in June 2009 and reached its peak in September 2009 (Figure 1).

Intense selection by the host immune system drives antigenic change which results in the continuous replacement of circulating strains with new variants to re-infect individuals and cause widespread ill-ness. Although the influenza A(H1N1)2009 virus has been circulating worldwide since April 2009, and the haemagglutinin (HA) antigenic sites have been under increasing antibody-mediated selection pressure [2], recent isolates were still antigenically similar to the vaccine virus A/California/7/2009 [3-5]. It is important to characterise the HA in order to monitor any emerg-ing variants while the virus continues to circulate in the community. Genetically, one of the characteristic differences between the epidemic viruses collected between March and September 2009 and the vaccine virus [6] was substitution at position 220 with almost all currently circulating viruses having S220T amino acid change (the amino acid positions of HA sequence are denoted using full HA coding region, i.e. amino acid position 18 corresponds to position 1 of the HA without the signal peptide) [7,8]. In addition to this mutation, the E391K substitution grew rapidly globally between

July and December 2009 [9] and two other substitu-tions, N142D and S202T, have recently been described in 2010 [4,5].

Here we describe temporal sequence changes in the HA gene of the influenza A(H1N1)2009 virus isolated in Hong Kong from 2009 to 2011.

Sample collection and sequence analysisFor this analysis, we included 338 full HA sequences of influenza viruses isolated from respiratory samples obtained from 40 public and private hospitals and clinics in Hong Kong between June 2009 and January 2011. The proportion of sequences analysed was in accordance with the positive isolation rate in each institution. Only one isolate from each patient was included. With the exception of June 2009, when only two full HA sequences were included at least four isolates from patients with either mild or severe respiratory illness were selected randomly per month. The PCR amplification and DNA sequencing of the full length of HA gene were per-formed using six different in-house designed primers: H1v-m0044-F (5’-AGTATACGACTAGCAAAAGCAGGGG-3’), H 1 v - 0 3 2 3 - R ( 5 ’ -TA A C A CG T T CC AT T G T C T G A -3’ ) , H1v - 0 8 9 8 - R ( 5 ’-T GGG T G T T T G AC A AG T T G TA -3’ ) , H1v-0805-F ( 5’-AGATATGCAT TCGCA ATGGA-3’), H 1v-1348-F( 5’-AGAACTTTGGACTACCACGA-3’), H 1v-1752-R ( 5’- CCGTGTC AGTAG A A AC A AGGGTGT T T-3’ ) . H 1v-m0044-F, H1v-0898-R, H1v-0805-F and H1v-1752-R were used as the PCR primers; in addition to these four primers, H1v-0323-R and H1v-1348-F were used as the sequencing primers.

Sequence data were compiled and edited using the Lasergene sequence analysis software pack-age (DNASTAR Inc). Multiple alignment of nucleotide sequences and translation of amino acid sequence was carried out by using BioEdit (http://www.mbio.ncsu.edu/bioedit/bioedit.html). In order to show the major evolutionary pattern of HA gene, only sequences shared by more than one isolate were included for the construction of a phylogenetic tree using MEGA (http://www.megasoftware.net/). According to this strat-egy, 33 sequences representing 217 isolates (64.2%,


217/338) were selected for phylogenetic analysis. One sequence (A/HongKong/2213/2010) that has been used as reference in EuroFlu Weekly Electronic Bulletin [10] and the National Institute for Medical Research [11] was also included for reference.

ResultsOver the study period, the amino acid at position 391 was either E or K. Phylogenetic analysis of the HA gene showed that the influenza A(H1N1)2009 viruses col-lected in Hong Kong clustered into two main branches characterised by this position (Figure 2).

With the emergence of E391K viruses in July 2009, the proportion of viruses with E391E fluctuated between 8% and 98% during the period from July 2009 to February 2010 and was gradually displaced by the evolving E391K viruses (Figure 3).

Within the main branch E391E, a sub-branch charac-terised by S145P reported previously [11] was also observed (Figure 2). The four strains A/Hong Kong/2213 (the reference strain used in EuroFlu Weekly Electronic Bulletin and the National Institute for Medical Research), A/Hong Kong/1886/2010, A/Hong Kong/2212/2010, A/Hong Kong/2200/2010 collected between April and July 2010 belonged to this sub-branch and all had V216A and I312V substitutions while A/Hong Kong/2200/2010 and A/Hong Kong/2212/2010 also had additional sub-stitutions K180T and P288S (not shown in Figure 2).

In the main branch with the E391K substitution, two sub-branches characterised by N142D and S202T muta-tion were observed (Figure 2). The isolates in the sub-branch characterised by N142D first appeared in March 2010 and its proportion appeared to peak in May 2010 and declined thereafter. The isolates in the sub-branch with the mutations S202T first appeared in July 2010 and their proportion increased sharply displacing the isolates with N142D in September 2010. This sub-branch continued to predominate since then (Figure 3).

DiscussionIn Hong Kong, with a sizable proportion of the popu-lation becoming infected during the first wave of pandemic in September in 2009 [12] and the implemen-tation of a vaccination programme using a monovalent vaccine in December 2009 [13], the resulting immuno-logical pressure may have driven virus evolution as shown by the displacement of E391E by E391K, a site important for membrane fusion [9], and the emer-gence of the two genetic sub-branches characterised by N142D and S202T amino acid substitutions involv-ing the antigenic sites Sa and Sb respectively. These antigenic sites contain many amino acids involved in neutralising epitopes near the receptor binding pock-ets [2]. All the genetic variants that emerged, how-ever, displayed similar antigenic characteristics when assessed by haemagglutination inhibition assay using A/California/07/2009 ferret antisera [3-5]. Although a single amino acid substitution involving one antigenic site may be sufficient to cause antigenic change, more

Figure 1Monthly influenza virus isolation rates by type and subtype, Centre for Health Protection, Department of Health, Hong Kong, 2009–2011

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

55%

60%

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan

2009 2010 2011

05001,0001,5002,0002,5003,0003,5004,0004,5005,0005,5006,0006,5007,0007,5008,0008,5009,0009,50010,00010,50011,00011,50012,00012,50013,00013,50014,00014,50015,00015,50016,00016,50017,00017,50018,00018,50019,00019,50020,00020,50021,00021,50022,00022,50023,00023,50024,00024,50025,000

Number of specimensInfluenza A(H1)Influenza A(H3)Influenza A(H1N1)2009Influenza B

Prop

ortio

n of

pos

itive

spe

cim

ens

Num

ber o

f spe

cim

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Figure 2Phylogenetic tree of the full-length haemagglutinin sequences of influenza A(H1N1)2009 virus circulating in Hong Kong from 2009 to 2011

Only the sequences shared by more than one isolate were included for the construction of a phylogenetic tree. The phylogenetic analysis was performed by use of the MEGA programme and the neighbour-joining method. The percentages of bootstrap frequencies over 50% are indicated. The tree was rooted with the vaccine strain A/California/07/2009. Amino acid substitutions in sub-branches are described under the internal branches. Each leaf node contains three sections: designated name of isolate, the time period isolates with this sequence were detected, the number of isolates with this sequence.The main branch substitution is shown in red colour and the sub-branch substitutions are shown in blue colour.


commonly antigenic drift variants of epidemiological importance have resulted from changes of at least four amino acids across two or more antigenic sites [14,15]. In fact, the prevalence of the influenza A(H1N1)2009 virus remained low in Hong Kong between March and December 2010 and was displaced during that period by the highly active influenza type A(H3N2) virus (Figure 1).

However, at the start of the traditional winter influenza season in Hong Kong in January 2011, the influenza A(H1N1)2009 virus belonging to the genetic sub-branch with E391K and S202T substitutions increased in number rapidly and became the predominant strain. While it is interesting to note the emergence of new genetic sub-branches and see how viruses circulating worldwide are selected and share the same HA muta-tions, mutations may often be an evolutionary ‘dead end’ and do not have much significance [16]. It is thus important that laboratory surveillance continues to include virus isolation and monitors the circulating viruses antigenically. Concurrent genetic surveillance would facilitate early detection of antigenic sites that are selected for the virus to escape immunological restraint.

References1. Garten RJ, Davis CT, Russell CA, Shu B, Lindstrom S, Balish

A, et al. Antigenic and genetic characteristics of swine-origin 2009 A(H1N1) influenza viruses circulating in humans. Science. 2009;325:197–201.

2. Igarashi M, Ito K, Yoshida R, Tomabechi D, Kida H, Takada A. Predicting the antigenic structure of the pandemic (H1N1) 2009 influenza virus hemagglutinin. PLoS One. 2010;5(1):e8553.

3. World Health Organization (WHO). Recommended viruses for influenza vaccines for use in the 2010-2011 northern hemisphere influenza season. Geneva:WHO; [Accessed 15 Feb 2011]. Available from: http://www.who.int/csr/disease/influenza/201002_Recommendation.pdf

4. Barr IG, Cui L, Komadina N, Lee RT, Lin RT, Deng Y, et al. A new pandemic influenza A(H1N1) genetic variant predominated in the winter 2010 influenza season in Australia, New Zealand and Singapore. Euro Surveill. 2010;15(42):pii=19692. Available from: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19692

5. Ellis J, Galiano M, Pebody R, Lackenby A, Thompson C, Bermingham A, et al. Virological analysis of fatal influenza cases in the United Kingdom during the early wave of influenza in winter 2010/11. Euro Surveill. 2011;16(1):pii=19760. Available from: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19760

6. Fereidouni SR, Beer M, Vahlenkamp T, Starick E. Differentiation of two distinct clusters among currently circulating influenza A(H1N1)v viruses, March-September 2009. Euro Surveill. 2009;14(46):pii=19409. Available from: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19409

7. Yang H, Carney P, Stevens J. Structure and Receptor binding properties of a pandemic H1N1 virus hemagglutinin. PLoS Curr. 2010;2:RRN1152.

8. Ikonen N, Haanpää M, Rönkkö E, Lyytikäinen O, Kuusi M, Ruutu P, et al. Genetic diversity of the 2009 pandemic influenza A(H1N1) viruses in Finland. PLoS One. 2010;5(10):e13329.

Figure 3Monthly proportion of influenza A(H1N1)2009 viruses characterised by E391E or E391K with either N142D or S202T, Centre for Health Protection, Department of Health, Hong Kong, 2009–2011 (n=338)

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Since some viruses did not have N142D or S202T, the sum of the proportion may not add up to 100%.


9. Maurer-Stroh S, Lee RT, Eisenhaber F, Cui L, Phuah SP, Lin RT. A new common mutation in the hemagglutinin of the 2009 (H1N1) influenza A virus. PLoS Curr. 2010;2:RRN1162.

10. World Health Organization (WHO). EuroFlu Weekly Electronic Bulletin. Influenza season 2010-2011. Geneva:WHO. [Accessed 15 Feb 2011]. Available from: http://www.euroflu.org/cgi-files/bulletin_v2.cgi

11. MRC National Institute for Medical Research. WHO Influenza Centre London. Report prepared for the WHO annual consultation on the composition of influenza vaccine for the Southern Hemisphere September 2010. [Accessed 15 Feb 2011]. Available from: http://www.nimr.mrc.ac.uk/documents/about/interim-report-sep-2010.pdf

12. Wu JT, Ma ES, Lee CK, Chu DK, Ho PL, Shen AL, et al. The infection attack rate and severity of 2009 pandemic H1N1 influenza in Hong Kong. Clin Infect Dis. 2010;51(10):1184–91.

13. Centre for Health Protection. Scientific Committee on Vaccine Preventable Diseases. Recommendations on Seasonal Influenza Vaccination for the 2010/11 Season. [Accessed 15 Feb 2011]. Available from: http://www.chp.gov.hk/files/pdf/recommendations_on_seasonal_influenza_vaccination_for_the_2010_11_season_eng.pdf

14. Ferguson NM, Galvani AP, Bush RM. Ecological and immunological determinants of influenza evolution. Nature. 2003;422(6930):428-33.

15. Fitch WM, Bush RM, Bender CA, Subbarao K, Cox NJ. The Wilhelmine E. Key 1999 Invitational lecture. Predicting the evolution of human influenza A. J Hered. 2000;91(3):183-5.

16. Steinhauer DA. Influenza A virus haemagglutinin glycoproteins. In Wang Q, Tao YJ editors. Influenza: Molecular Virology. Wymondham: Caister Academic Press; 2010. p. 69-108.


Surveillance and outbreak reports

Hepatitis A outbreak predominantly affecting men who have sex with men in Northern Ireland, October 2008 to July 2009

O Sfetcu ([email protected])1,2, N Irvine1, S L Ngui3, C Emerson4, C McCaughey5, P Donaghy1

1. Health Protection Service, Public Health Agency, Northern Ireland, United Kingdom2. European Programme for Intervention Epidemiology Training (EPIET), European Centre for Disease Prevention and Control (ECDC), Stockholm, Sweden3. Virus Reference Department (VRD), Health Protection Agency, London, United Kingdom4. Genito-Urinary Medicine Clinic, Royal Hospitals, Belfast HSC Trust, Northern Ireland, United Kingdom5. Regional Virus Laboratory, Royal Hospitals, Belfast HSC Trust, Northern Ireland, United Kingdom

Citation style for this article: Sfetcu O, Irvine N, Ngui SL, Emerson C, McCaughey C, Donaghy P. Hepatitis A outbreak predominantly affecting men who have sex with men in Northern Ireland, October 2008 to July 2009. Euro Surveill. 2011;16(9):pii=19808. Available online: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19808


We describe an outbreak of hepatitis A which evolved in Northern Ireland between October 2008 and July 2009, against a background of large concurrent hepati-tis A outbreaks in various parts of Europe. Thirty-eight cases were defined as outbreak cases using a strati-fied case definition; 36 were males with a median age of 29 years and of the 28 males whose sexual orienta-tion was known, 26 were men who have sex with men (MSM). Detailed descriptive epidemiology data col-lected through standardised questionnaires, together with sequencing of a 289 bp fragment of the VP1/2PA region of the virus, significantly aided the under-standing of the spread of the outbreak when non-MSM cases occurred. The sequence of the outbreak strain, genotype IA, was indistinguishable from that involved in a large outbreak in the Czech Republic. Although seeded in a generally susceptible Northern Ireland population, the outbreak remained mostly contained in MSM, showing this sub-population to be the most vulnerable despite ongoing hepatitis A vaccination programmes in genito-urinary medicine clinics.

Introduction Hepatitis A is an acute, usually self-limiting disease caused by infection with the hepatitis A virus (HAV) [1]. Transmission is usually by the faecal-oral route, includ-ing person-to-person spread, contaminated water or food products, but has also been associated with out-breaks in injecting drug users and men who have sex with men (MSM) [2-4]. The mean incubation period is 28 days (range 15-50 days). Asymptomatic and mild disease is common in children but the majority of adults who become infected are symptomatic, often with acute jaundice [5]. With increasing hygiene in developed countries, hepatitis A infection has become much less common leading to populations with a large majority of people who are not immune. One conse-quence of this is that proportionately more suscepti-ble adults are infected when outbreaks do occur, and

consequently more severe clinical symptoms are seen [6]. Peak infectivity occurs two weeks before onset of jaundice and falls rapidly thereafter. The diagnosis is made by serological detection of anti-HAV IgM which becomes detectable at the onset of symptoms and can persist for up to six months. HAV RNA is also a marker of acute infection and is present in the patient’s serum prior to the appearance of anti-HAV IgM [7]. In regions with a low incidence of HAV infection, sequencing of HAV RNA can be used to link apparently sporadic cases and outbreaks [8].

Monovalent and combined hepatitis A vaccines have been available since 1995 and are all highly immuno-genic. Nearly 100% of adults will develop protective levels of antibody within one month after a single dose of vaccine [9]. In the United Kingdom (UK), pre-exposure vaccination is recommended for selected risk groups, including MSM who have multiple part-ners, particularly during periods when outbreaks are occurring [5,10]. Hepatitis A vaccine alone or combined with human normal immunoglobulin can be effectively used in preventing infections in contacts of cases, if administered within 14 days of the onset of symptoms in the index case [5]. Since 2006, MSM attending the healthcare services specialised in sexually transmitted infections, the genito-urinary medicine (GUM) clinics, in Northern Ireland have been offered combined hepa-titis A and B vaccination, in line with guidance from the British Association of Sexual Health and HIV-Clinical Effectiveness Group (UK BASHH) [10]. However, vacci-nation coverage among MSM is not known.

Hepatitis A is a notifiable disease in Northern Ireland (population 1,775,000). Patients presenting with clini-cal symptoms which are confirmed by the Regional Virology Laboratory are reported to the regional sur-veillance unit of the Public Health Agency. Since 2003, there have been between zero and seven sporadic cases


reported annually (Figure 1). After a decade of decrease of hepatitis A incidence in Europe an outbreak began in the autumn of 2007 in Latvian injecting drug users fol-lowed by spread into the general population and lasted until the end of 2008 [11]. In autumn 2008, the Czech and Slovak Republics reported large outbreaks initially in injecting drug users and Roma communities respec-tively, followed by community spread within the gen-eral population [12,13]. Subsequently outbreaks among MSM have been reported from Spain (Barcelona) [14] and Italy (Rome) [15].

In October 2008, two hepatitis A cases were reported in Northern Ireland, followed by another four in November after a median time interval of 30 days. All cases were in MSM, aged between 25 and 40 years. An outbreak control team was convened in December 2008 to coordinate outbreak investigations and to undertake control measures. An urgent letter was issued to alert healthcare providers. The aim of the epidemiological study was to describe the course of the outbreak and identify any possible common exposures for further investigation.

Methods Epidemiological investigationInitially, an outbreak case was defined as any resi-dent of Northern Ireland who tested positive for anti-HAV IgM after 1 October 2008. In January 2009 cases began to occur in heterosexual males and females. At this time the outbreak control team asked for all posi-tive samples to be sequenced in order to understand the progress of the outbreak which transcended the MSM population. Unfortunately, as sequencing of anti-HAV IgM-positive samples was not a routine activity at the time, a number of samples had insufficient volume for sequencing and others had been discarded. After sequencing information became available a stratified case definition was used to describe the outbreak. A possible outbreak case was classified as a resident of Northern Ireland who tested positive for anti-HAV IgM

after 1 October 2008. A possible case was upgraded to a confirmed outbreak case if the case was found after sequencing to have the genotype IA outbreak strain (referred to hereafter as the outbreak strain). Any case found to be epidemiologically linked to a con-firmed case was defined as a probable outbreak case. A case was considered to be epidemiologically linked if they had been sharing the same household or had been in intimate contact with a confirmed case in the two months before becoming ill. A case was defined as sporadic if any non-outbreak strain was identified in an anti-HAV IgM-positive resident of Northern Ireland dur-ing the study period.

A standardised questionnaire administered by environ-mental health officers, part A, was used to collect the patients’ demographic and clinical characteristics (age, sex, sexual orientation, occupation, place of residence, nationality, symptoms, onset date, and hospitalisa-tion status), as well as details of selected food expo-sures (consumption of shellfish, raw salad, take-away food or eating outside the home), travel abroad, and contact with a symptomatic hepatitis case in the two months before onset of illness. Part B of the standard-ised questionnaire was administered by GUM special-ists and used to collect details of sexual orientation, number of sexual partners, condom use, visiting and/or having sex in gay venues, and other sexual behav-iours, in the two months prior to onset of symptoms. Diagnoses of new and past co-infections were also col-lected. The questionnaires were collated at the Public Health Agency surveillance unit and data entered into an enhanced surveillance database and STATA (Stata Statistical Software: Release 10, StataCorp 2007) was used to produce descriptive statistics.

Virological analysisSerological diagnosis was performed by the regional virology laboratory at Royal Victoria Hospital in Belfast using the Abbott Architect anti-HAV IgM assay. Where residual sample volume was available this was for-warded to the virus reference department (VRD) of the Health Protection Agency for HAV RNA detection and sequencing. The HAV RNA was extracted from serum and reverse-transcribed into cDNA by random hexamers. Amplification of the VP1/2PA junction was performed by nested PCR as described previously [16] using primers HAV6, HAV7 in this reference for primary amplification, and BR-9 and BR-5 for secondary amplifi-cation. The PCR products were sequenced, resulting in a 289 bp sequence, and genotype assignment was pre-formed by alignment and comparison with sequences of known genotype in MegAlign (DNASTAR) followed by confirmation using BLAST (http://www.ncbi.nlm.nih.gov/blast/).

Results Descriptive epidemiologyFrom 4 October 2008 to 1 July 2009, a total of 43 acute hepatitis A cases were reported; of those, 38 were clas-sified as outbreak cases and five as sporadic cases.

Figure 1Laboratory reports of hepatitis A, Northern Ireland, 1998–2009 (n=241)

HAV: hepatitis A virus; IgM: immunglobulin M.

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Outbreak cases (n=38)Of the 38 outbreak cases, 24 met the case definition for a confirmed outbreak case, 10 cases were defined as possible and four were classified as probable. The basis for the classification of the three of the four prob-able cases was that they were MSM who had house-hold contact with confirmed cases. The fourth probable outbreak case was a man whose female sexual partner was found to have the outbreak strain.

Thirty-six cases were male, with a median age of 29 years (range: 18–51 years). Information on sexual orientation was available for 28 males, 26 of whom were MSM. All ten possible cases were MSM. With the exception of the index case who was from another European country, all other cases were British or Irish citizens. Of the 33 cases for whom occupational details were available, eight were food-handlers and two were healthcare workers. The eight food-handlers worked in eight different retail premises none of which were rec-ognised gay venues. Information on clinical symptoms was available for 31 patients, 30 of whom presented with jaundice. Other symptoms were nausea (n=21), loss of appetite (n=17), abdominal pain (n=16), fatigue (n=14), and fever (n=13). Twenty-five cases were admit-ted to hospital.

Food history was recorded for 18 cases. No common food product, take-away or other catering establish-ments was identified. None of the eight premises where the food-handling cases worked during their incubation period was named by any other case.

Seven of the 31 cases with known travel history reported travel abroad in the two months prior to ill-ness. Two MSM cases travelled in the four weeks prior to onset of symptoms, one to Prague, Czech Republic, and one to Dublin, Republic of Ireland. The other five

cases travelled within the UK, two of them in the two weeks before the onset of symptoms.

Twenty of the outbreak cases, all males, attended a GUM clinic where they completed a standardised ques-tionnaire and were screened for coinfections. Eight cases, all MSM, were diagnosed with coinfections on that occasion: three with syphilis, one with human immunodeficiency virus (HIV), one with HIV and gonor-rhoea, and three with non-specific urethritis.

Data on sexual behaviour in the two months prior to onset of illness was only available for 18 of the male cases who attended GUM services. Twelve reported having sex with another male in the two months before illness; the median number of partners was one (range 1–3). Of the 12 male cases who reported having anal sex with another man, only six declared consistent con-dom use (‘always’). Of the remaining six males report-ing no sexual contact in the two-month period, three had visited gay clubs during that time.

Information on history of hepatitis A vaccination was not available for the cases.

Sporadic cases (n=5)From 14 October 2008 to 8 June 2009, five sporadic cases were reported. Three cases were male, aged 20-49 years, and two female, aged 20-24 years. Two were MSM whose dates of onset were separated by an interval of six months, and who reported travel to Budapest, Hungary, and Barcelona, Spain, in the two months prior to onset of illness. The third male case declared only shellfish consumption as a risk factor. Two female cases reported travel to England and Africa during the incubation period.

VirologyTwenty-nine of the 43 anti-HAV IgM-positive specimens were available for HAV RNA detection and sequencing. Sequences of the 289 bp VP1/2PA fragment derived from 23 of these samples were indistinguishable from

Figure 2Hepatitis A cases by specimen date and genotype, Northern Ireland, 4 October 2008-1 July 2009 (n=43)

HAV: hepatitis A virus; IgM: immunglobulin M.

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Confirmed outbreak cases: anti-HAV IgM-positive, the outbreak IA genotype (n=24)

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Possible outbreak cases: anti-HAV IgM-positive, genotype not available (n=10)

Sporadic cases: anti-HAV IgM positive, different genotypes (n=5)


each other and of genotype IA; this was designated as the outbreak strain. A further sample had a 99.7% homology (one mutation in the 289 bp fragment) to the outbreak strain. Given the low incidence of HAV in Northern Ireland and the common risk of MSM we took this to be an indication that this strain was related to the outbreak. The outbreak strain was unlike any strain previously sequenced at the VRD. Comparison of the outbreak strain with other strains isolated from recent outbreaks in Europe found it to be indistinguishable over 289 bp from the strain involved in the outbreak in the Czech Republic in 2008 (kindly provided by H Vennema).

Viruses isolated from two non-outbreak MSM cases shared the same sequence; the two isolates belonged to genotype IA but had only 96.9% homology to the outbreak strain. This strain had been observed at the VRD in other sporadic cases but these had all occurred

in mainland England. Comparison of this sequence with other European outbreak strains found it to be indistinguishable from the strain involved in the MSM community in Barcelona, in 2008 and 2009 (kindly pro-vided by R Pinto).

The remaining three samples sequenced were geno-type IB and were all distinguishable from each other. The homologies of these strains to the outbreak strain were 91.7%, 90.3% and 84.1%.

Control measures Each case was visited at home or interviewed by tele-phone by the environmental health officers, in order to identify any environmental risk factors and exposures and to trace close contacts. All cases were referred to GUM clinics and their family and sexual contacts were referred to the general practitioner or to the GUM clinic to receive hepatitis A vaccine and human normal immu-noglobulin as appropriate. In cases known to be food handlers a risk assessment of the food premise was conducted and preventive information was provided. Outreach activities were undertaken in two of the most frequented gay venues in Belfast over a period of two months: hepatitis vaccines were offered according to personal history, and testing was offered for HIV, syph-ilis, hepatitis and chlamydia infection. Information on hepatitis A and safe sex were distributed in gay venues with the assistance of ‘Rainbow’ Sexual Health Project volunteers using fliers and posters. Information on the outbreak and details on hepatitis A clinical pres-entation and prevention were posted on their web-site (http://www.rainbow-project.org).

Discussion This is the first outbreak of hepatitis A in Northern Ireland following a decade of low incidence. It occurred against a background of large concurrent European outbreaks all reported to have started in at-risk groups followed by spread into the general population (Figure 3) [2-4,10,12,13]. The index case became ill after hav-ing travelled to Prague in September 2008, when the Czech outbreak was reaching its peak incidence [12]. Comparison of the HAV RNA sequence derived from this outbreak with that of the Czech virus appears to confirm an association.

Contrary to the experience with other European out-breaks occurring in 2008-2009 in the Czech Republic, Latvia and Slovakia, the outbreak reported here remained largely confined to the MSM sub-popula-tion, despite the majority of the general population in Northern Ireland being susceptible to HAV infection [17]. The potential for spread to the community was highlighted by the fact that cases occurred in food handlers and healthcare workers. The eight food han-dlers in particular had the potential to disseminate the virus widely given that they worked at eight dif-ferent premises. Prompt public health action through contact tracing and post exposure prophylaxis, pub-licity within the gay community and the provision of

Figure 3Hepatitis A outbreak in Northern Ireland (n=40), the source outbreak in the Czech Republic (n=1,580) and the concurrent outbreak in Barcelona (n=122), 2008-2009

Source of data for the cases in the Czech Republic and Barcelona: graphs published in [9,12].

Outbreak in the Czech Republic , genotype IA ,July-December 2008

Outbreak in Barcelona, genotype IA (distinct sequence),September 2008-March 2009

Outbreak in Northern Ireland, genotype IA (Czech sequencen=38, Barcelona sequence n=2), October 2008-July 2009

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outreach sessions at selected implicated venues have contributed to the apparent control of the outbreak. Collaboration between public health, environmental health, GUM specialists and the voluntary sector was essential.

Our study did not allow an in-depth ascertainment of transmission pathways, given that less than half of the outbreak cases returned the questionnaires on sexual risk behaviour. Similarly we were unable to document a specific venue associated with this outbreak. Notably, three MSM cases reported they had not had sex in the two month prior to illness but had visited gay venues. This raises the possibility that transmission may have occurred through environmental contamination, a find-ing also noted in other outbreaks [18]. Transmission via food does not seem likely as no common food source or catering venue (among food handler cases or subse-quent cases) was identified.

UK national policy recognises that MSM are a vulner-able group for hepatitis A and recommends they are offered pre-exposure vaccination at times of ongoing outbreaks [5]. Our experience shows this is important even in a region of low incidence, given the potential for rapid seeding of outbreaks from elsewhere.

This is further emphasised by the finding of two spo-radic MSM cases during this outbreak with a common sequence indistinguishable from that implicated in the large MSM outbreak in Barcelona. That neither of them seeded an outbreak suggests either that they did not have sex in Northern Ireland while infectious (probable explanation for the case in October 2008) or that the preventive control measures were already effective and the MSM community alerted (probable explanation for the case in May 2009).

Although sequencing of HAV RNA did not significantly aid the management of the outbreak, it enabled us to define the sporadic cases and demonstrate that the outbreak was not spreading to the general community. In this setting of low HAV incidence, HAV sequencing was a valuable tool in linking apparently unlinked cases to the outbreak. Sequencing results derived from the outbreak enabled us to link the outbreak in Northern Ireland to the larger outbreak in the Czech Republic and to show that two sporadic cases, only one of which had been to Spain, shared the same strain circulat-ing in the MSM outbreak in Spain. Comparison of the sequences from these two large outbreaks was only possible thanks to the sharing of information from the laboratories that performed the sequencing because at the time, there was no specific database for HAV sequences in the public domain.

ConclusionThis outbreak highlights the importance of timely diag-nosis and reporting of cases to allow for appropriate and targeted control measures. The high rate of other sexually transmitted infections (STI) among MSM

cases confirms the worth of STI testing during such an outbreak. Awareness of the value and availability of hepatitis A vaccination among MSM in Northern Ireland must be increased. Sequencing the virus and collaborating with other countries involved in similar epidemics helped us understand how this outbreak spread; sequencing of all HAV cases has continued since this time. It has subsequently come to light that HAV sequences can be sent to the Food-borne Viruses in Europe (FBVE) network for comparison with their database [19]: this network is currently making its HAV sequence database publically available.

AcknowledgementsThe authors acknowledge the valuable contribution of all the Outbreak Control Team members, Environmental Health Officers, Genito-Urinary Clinic staff, and The “Rainbow “Project volunteers. Special thanks are expressed to Dr Vratislav Nemecek, Dr Harry Vennema and Dr Rosa Pinto for enabling the comparison of sequences from the Czech and Spanish outbreaks respectively.

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Infectious Diseases 7th edition. Chapter 173. United Kingdom: Churchill Livingstone; 2009

2. Payne L, Coulombier D. Hepatitis A in the European Union: responding to challenges related to new epidemiological patterns. Euro Surveill. 2009;14(3):pii=19101. Available from: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19101

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11. Perevoščikovs J, Lucenko I, Magone S, Brila A, Curikova J, Vennema H. Community-wide outbreak of hepatitis A in Latvia in 2008 – an update. Euro Surveill. 2009;14(3):pii=19092. Available from: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19092

12. Cástková J, Beneš C. Increase in hepatitis A cases in the Czech Republic in 2008 – an update. Euro Surveill. 2009;14(3):pii=19091. Available from: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19091


13. Hrivniaková L, Sláčiková M, Kolcunová S. Hepatitis A outbreak in a Roma village in eastern Slovakia, August-November 2008 . Euro Surveill. 2009;14(3):pii=19093. Available from: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19093

14. Tortajada C, de Olalla PG, Pinto RM, Bosch A, Caylà J. Outbreak of hepatitis A among men who have sex with men in Barcelona, Spain, September 2008 – March 2009. Euro Surveill. 2009;14(15):pii=19175. Available from: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19175

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Perspectives

Evaluation of syndromic surveillance in the Netherlands: its added value and recommendations for implementation

C C van den Wijngaard ([email protected])1, W van Pelt1, N J Nagelkerke2, M Kretzschmar1, M P Koopmans1,3

1. Rijksinstituut voor Volksgezondheid en Milieu (National Institute for Public Health and the Environment, RIVM), Bilthoven, the Netherlands2. United Arab Emirates University, Al-Ain, United Arab Emirates3. Erasmus Medical Center, Rotterdam, the Netherlands

Citation style for this article: van den Wijngaard CC, van Pelt W, Nagelkerke NJ, Kretzschmar M, Koopmans MP. Evaluation of syndromic surveillance in the Netherlands: its added value and recommendations for implementation. Euro Surveill. 2011;16(9):pii=19806. Available online: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19806


In the last decade, syndromic surveillance has increas-ingly been used worldwide for detecting increases or outbreaks of infectious diseases that might be missed by surveillance based on laboratory diagnoses and notifications by clinicians alone. There is, however, an ongoing debate about the feasibility of syndromic surveillance and its potential added value. Here we present our perspective on syndromic surveillance, based on the results of a retrospective analysis of syndromic data from six Dutch healthcare registries, covering 1999–2009 or part of this period. These registries had been designed for other purposes, but were evaluated for their potential use in signal-ling infectious disease dynamics and outbreaks. Our results show that syndromic surveillance clearly has added value in revealing the blind spots of traditional surveillance, in particular by detecting unusual, local outbreaks independently of diagnoses of specific pathogens, and by monitoring disease burden and vir-ulence shifts of common pathogens. Therefore we rec-ommend the use of syndromic surveillance for these applications.

Background In the last decade, syndromic surveillance has increas-ingly been implemented to detect and monitor infec-tious disease outbreaks, as early detection and control may well mitigate the impact of epidemics [1-3]. In the United Kingdom, for example, a telephone health hel-pline (NHS Direct) is used for syndromic surveillance [1]; in France, a syndromic surveillance system based on hospital emergency data has been deployed [4]; and in North America several syndromic surveillance systems exist using data such as telephone helpline calls [5] and hospital emergency department visits [2,6]. Traditional outbreak detection based on astute clinicians and laboratory diagnoses can have blind spots for emerging diseases, because patients report-ing with common symptoms (e.g. pneumonia) associ-ated with the disease may not alarm clinicians, and uncommon or new pathogens can remain undetected

by laboratories (such as initially happened in the out-break of severe acute respiratory syndrome (SARS) in 2003). Syndromic surveillance may reveal such blind spots of traditional surveillance by monitoring eleva-tions of common symptoms or clinical diagnoses such as shortness of breath or pneumonia.

The increasing use of syndromic surveillance seems driven by two factors: (i) high-profile disease events (e.g. the 2001 anthrax attacks, 2003 SARS outbreak, the threat of a new influenza pandemic, excess mortal-ity due to heat waves) stressing the need for improved early warning surveillance; and (ii) the increased avail-ability of electronic healthcare data, making large-scale monitoring of non-specific health indicators increasingly feasible.

There is, however, an ongoing debate about the added value of syndromic surveillance. Some scepticism exists about the potential workload it may generate if used for real-time outbreak detection (i.e. if the sys-tem creates many false-positive signals) [7]. In the Netherlands, this debate has led to a research project to evaluate the potential value of syndromic surveil-lance for infectious disease surveillance and control, and to make recommendations for its implementation. The questions addressed were: (i) what syndromic data types track known dynamics of infectious diseases in the general population, and thus will also be likely to reflect emerging pathogen activity? (ii) can syndromic surveillance improve the monitoring of disease burden and/or detect shifts in the virulence of common patho-gens? (iii) can syndromic surveillance detect local out-breaks that have a limited number of signals in time, independent of laboratory detection of the causative pathogens?

We addressed these questions by retrospectively ana-lysing syndromic data from six Dutch healthcare regis-tries, and also by ad hoc use of syndromic surveillance for upcoming infectious disease problems. To select


Tabl

e 1

Synd

rom

ic d

ata

regi

stri

es in

clud

ed in

the

synd

rom

ic su

rvei

llanc

e ev

alua

tion

stud

y, th

e N

ethe

rland

s

Data

type

Regi

stry

Perio

d ev

alua

ted

Popu

latio

n co

vera

ge(%

)aSy

ndro

me

info

rmat

ionb

Data

ana

lyse

dIn

tern

atio

nal c

odin

g sy

stem

Pro

spec

tive

impl

emen

tatio

n of

su

rvei

llanc

e

Abse

ntee

ism

Na

tiona

l abs

ente

eism

regi

stry

by

Sta

tistic

s Ne

ther

land

s (C

BS)[8

]20

02–0

380

(of t

he w

orki

ng

popu

latio

n of

8

mill

ion)

Empl

oyee

s re

porte

d si

ck,

no fu

rther

med

ical

info

rmat

ion

Sick

leav

e re

ports

by

empl

oyer

s–

NAc

Gene

ral

prac

titio

ner

cons

ulta

tions

Neth

erla

nds

Info

rmat

ion

Netw

ork

of G

ener

al P

ract

ice

(LIN

H, b

y NI

VEL-

the

Neth

erla

nds

Inst

itute

for

Heal

th S

ervi

ces

Rese

arch

) [9]

2001

–04

1–2d

Sym

ptom

s an

d di

agno

ses

indi

catin

g in

fect

ious

dis

ease

Sym

ptom

s an

d di

agno

ses

reco

rded

in g

ener

al p

ract

ice

or

tele

phon

e co

nsul

tatio

ns,

and

hom

e vi

sits

Inte

rnat

iona

l Cla

ssifi

catio

n of

Prim

ary

Care

(ICP

C)

Real

-tim

e sy

stem

cu

rrent

ly b

eing

im

plem

ente

d

Phar

mac

y pr

escr

iptio

ns

Foun

datio

n fo

r Pha

rmac

eutic

al

Stat

istic

s (S

FK) [

10]

2001

–03

85Pr

escr

ibed

med

icat

ions

in

dica

ting

infe

ctio

us d

isea

se

Pres

crip

tion

med

icat

ions

di

spen

sed

in D

utch

ph

arm

acie

s

Anat

omic

al T

hera

peut

ic

Chem

ical

Cla

ssifi

catio

n Sy

stem

(ATC

)

Curre

ntly

mon

thly

da

ta u

pdat

es a

re

feas

ible

in

ad h

oc p

ublic

hea

lth

situ

atio

ns

Hosp

italis

atio

nsDu

tch

Natio

nal M

edic

al

Regi

ster

(LM

R) b

y Du

tch

Hosp

ital D

ata

(DHD

) [11

]19

99–2

007

99Ge

nera

l sy

mpt

oms

and

diag

nose

s an

d sp

ecifi

c bi

olog

ical

age

nt d

iagn

oses

Disc

harg

e an

d se

cond

ary

diag

nose

s an

d da

te o

f ho

spita

lisat

ion

Inte

rnat

iona

l Cl

assi

ficat

ion

of D

isea

ses,

Ni

nth,

Revi

sion

Clin

ical

M

odifi

catio

n (IC

D-9-

CM)

No p

rosp

ectiv

e im

plem

enta

tion

poss

ible

in th

e sh

ort t

erm

(ann

ual

data

upd

ates

will

co

ntin

ue)

Labo

rato

ry

subm

issi

ons

(neg

ativ

e an

d po

sitiv

e re

sults

)

Natio

nal I

nfec

tious

Dis

ease

s In

form

atio

n Sy

stem

(ISI

S-M

ML)

[1

2]20

01–0

416

Subm

issi

ons

for s

peci

fic

mic

robi

olog

ical

dia

gnos

tic

test

s

Labo

rato

ry s

ubm

issi

on

requ

ests

for d

iagn

ostic

test

ing

–NA

c

Mor

talit

y Ca

use

of d

eath

and

cru

de

mor

talit

y re

gist

ry b

y Sta

tistic

s Ne

ther

land

s (C

BS)[1

3]

1999

–200

4 fo

r ca

use-

of-d

eath

da

ta;

1999

–200

9 fo

r cr

ude

mor

talit

y da

ta

100

Gene

ral s

ympt

oms

and/

or

diag

nose

s an

d bi

olog

ical

ag

ent-s

peci

fic d

iagn

oses

Date

of d

eath

, prim

ary

caus

e of

dea

th, c

ompl

icat

ing

and

othe

r add

ition

al c

ause

s of

de

ath

Inte

rnat

iona

l Cla

ssifi

catio

n of

Dis

ease

s, 10

th re

visi

on

(ICD-

10)

Curre

ntly

wee

kly

crud

e m

orta

lity

surv

eilla

nce

(pilo

t pha

se)

NA:

not

app

licab

le.

a Cal

cula

ted

as a

per

cent

age

of th

e to

tal p

opul

atio

n (1

6.3

mill

ion

in 2

006

[14]

), un

less

oth

erw

ise

indi

cate

d.

b Det

aile

d sy

ndro

me

defin

ition

s av

aila

ble

from

the

auth

ors

on re

ques

t.c T

he la

bora

tory

sub

mis

sion

s re

gist

ry (I

SIS-

MM

L) a

nd th

e na

tiona

l abs

ente

eism

regi

stry

cea

sed

to e

xist

dur

ing

our s

tudy

.d T

he G

P re

gist

ry c

over

age

will

incr

ease

to 5

% in

the

next

few

yea

rs a

s pa

rt o

f the

Sur

veill

ance

Net

wor

k Ne

ther

land

s (S

UNN)

, whi

ch is

pre

dom

inan

tly fo

cuse

d on

influ

enza

sur

veill

ance

[15]

.


Tabl

e 2

Trac

king

of i

nfec

tious

dis

ease

dyn

amic

s usi

ng th

ree

synd

rom

es a

nd si

x da

ta ty

pes f

rom

hea

lthca

re re

gist

ries

, syn

drom

ic su

rvei

llanc

e ev

alua

tion

stud

y, th

e N

ethe

rland

s

Data

type

sRe

spira

tory

syn

drom

esGa

stro

ente

ritis

syn

drom

esNe

urol

ogic

al s

yndr

omes

Abse

ntee

ism

Win

ter p

eaks

con

curre

nt w

ith p

eaks

in in

fluen

za v

irus,

RSV

an

d ot

her r

espi

rato

ry p

atho

gens

; 68%

of v

aria

tions

exp

lain

ed

by re

spira

tory

pat

hoge

ns; 2

wee

ks a

head

of R

SV, 4

–5 w

eeks

ah

ead

of in

fluen

za [1

9]No

t eva

luat

eda

Not e

valu

ated

a

Gene

ral

prac

titio

ner

cons

ulta

tions

Win

ter p

eaks

con

curre

nt w

ith p

eaks

in in

fluen

za, R

SV a

nd

othe

r res

pira

tory

pat

hoge

ns: 8

6% o

f var

iatio

ns e

xpla

ined

by

resp

irato

ry p

atho

gens

, 1 w

eek

behi

nd R

SV, 1

–2 w

eeks

ahe

ad

of in

fluen

za [1

9]

Win

ter p

eaks

and

sum

mer

pea

ks c

oncu

rrent

with

rota

viru

s an

d Sh

igel

la/S

alm

onel

la/C

ampy

loba

cter

pea

ks, r

espe

ctiv

ely:

29%

of

var

iatio

ns e

xpla

ined

by

gast

roen

tera

l pat

hoge

ns (5

1% fo

r th

ose

aged

0–4

yea

rs, t

wo

wee

ks a

head

of r

otav

irus)

[20]

; an

incr

ease

in w

inte

r of 2

002/

03 p

ossi

bly

rela

ted

to

noro

viru

s ac

tivity

[21]

No c

lear

refle

ctio

n of

kno

wn

dise

ase

dyna

mic

s

Phar

mac

y pr

escr

iptio

ns

Win

ter p

eaks

con

curre

nt w

ith p

eaks

in in

fluen

za, R

SV a

nd

othe

r res

pira

tory

pat

hoge

ns: 8

0% o

f var

iatio

ns e

xpla

ined

by

resp

irato

ry p

atho

gens

; 1 w

eek

behi

nd R

SV, 0

–2 w

eeks

ahe

ad

of in

fluen

za [1

9]

Rela

tivel

y lo

w w

inte

r pea

ks a

nd h

ighe

r sum

mer

pea

ks

conc

urre

nt w

ith ro

tavi

rus

and

Sh

igel

la/S

alm

onel

la/C

ampy

loba

cter

pea

ks, r

espe

ctiv

ely

Not e

valu

ated

b

Hosp

italis

atio

ns

Win

ter p

eaks

con

curre

nt w

ith p

eaks

in in

fluen

za, R

SV a

nd

othe

r res

pira

tory

pat

hoge

ns; 8

4% o

f var

iatio

ns e

xpla

ined

by

resp

irato

ry p

atho

gens

; in

conc

urre

nce

with

RSV

, 1–2

wee

ks

ahea

d of

influ

enza

[19]

Rela

tivel

y hi

gh w

inte

r pea

ks a

nd lo

wer

sum

mer

pea

ks

conc

urre

nt w

ith ro

tavi

rus

and

Shig

ella

/Sal

mon

ella

/Ca

mpy

loba

cter

pea

ks, r

espe

ctiv

ely:

40%

of v

aria

tions

exp

lain

ed

by g

astro

ente

ral p

atho

gens

(85%

for t

hose

age

d 0–

4 ye

ars

one

wee

k ah

ead

of ro

tavi

rus)

[20]

; an

incr

ease

in w

inte

r of 2

002/

03 p

ossi

bly

rela

ted

to n

orov

irus

activ

ity [2

1]

The

gene

ral n

euro

logi

cal s

yndr

ome

did

not c

lear

ly re

flect

kn

own

dise

ase

dyna

mic

.A

vira

l neu

rolo

gica

l syn

drom

e sh

owed

sum

mer

pea

ks

conc

urre

nt w

ith e

nter

oviru

s pe

aks:

62%

of i

ts v

aria

tions

was

ex

plai

ned

by e

nter

oviru

s no

tifica

tions

[22]

Labo

rato

ry

subm

issi

ons

(neg

ativ

e an

d po

sitiv

e re

sults

)

Win

ter p

eaks

con

curre

nt w

ith p

eaks

in in

fluen

za, R

SV a

nd

othe

r res

pira

tory

pat

hoge

ns: 6

1% o

f var

iatio

ns e

xpla

ined

by

resp

irato

ry p

atho

gens

; 2 w

eeks

beh

ind

RSV,

0–1

wee

k ah

ead

of in

fluen

za [1

9]

Rela

tivel

y lo

w w

inte

r pea

ks a

ndhi

gher

sum

mer

pea

ks c

oncu

rrent

with

rota

viru

s an

d Sh

igel

la/S

alm

onel

la/C

ampy

loba

cter

pea

ks, r

espe

ctiv

ely

No c

lear

refle

ctio

n of

kno

wn

dise

ase

dyna

mic

s

Mor

talit

y

Win

ter p

eaks

con

curre

nt w

ith p

eaks

in in

fluen

za, R

SV a

nd

othe

r res

pira

tory

pat

hoge

ns; 7

8% o

f var

iatio

ns e

xpla

ined

by

resp

irato

ry p

atho

gens

; 3 w

eeks

beh

ind

RSV,

0–1

wee

k ah

ead

of in

fluen

za [1

9]

No o

bvio

us re

flect

ion

of k

now

n se

ason

al p

atho

gen

activ

ity:

an in

crea

se in

win

ter 2

002/

03 p

ossi

bly

rela

ted

to

noro

viru

s ac

tivity

[21]

No

cle

ar re

flect

ion

of k

now

n di

seas

e dy

nam

ics

RSV:

resp

irato

ry s

yncy

tial v

irus.

The

tabl

e su

mm

aris

es p

er d

ata

and

synd

rom

e ty

pe w

heth

er s

yndr

ome

peak

s co

ncur

red

with

pat

hoge

n pe

aks,

wha

t per

cent

age

of th

e sy

ndro

me

varia

tions

is e

xpla

ined

by

varia

tions

in p

atho

gen

coun

ts,

and

wha

t the

diff

eren

ces

in ti

mel

ines

s w

ere

betw

een

the

synd

rom

e an

d pa

thog

en d

ata.

The

latt

er a

re a

sses

sed

by th

e op

timis

ed la

gs o

f pat

hoge

n co

unts

in ti

me-

serie

s m

odel

s th

at e

xpla

in th

e sy

ndro

me

varia

tion

[19]

.a T

he a

bsen

teei

sm d

ata

lack

ed m

edic

al in

form

atio

n, b

ut it

s tim

e se

ries

refle

cted

resp

irato

ry p

atho

gen

activ

ity;

ther

efor

e th

e ot

her s

yndr

omes

wer

e no

t eva

luat

ed fo

r thi

s re

gist

ry.

b No

data

on

phar

mac

y pr

escr

iptio

ns s

peci

fic fo

r neu

rolo

gica

l con

ditio

ns w

ere

avai

labl

e fo

r ana

lysi

s.


potential syndromic data sources, we asked Dutch healthcare registry owners to provide information on predefined criteria (coverage, timeliness of data entry and potential for transition to real-time data availabil-ity). Table 1 shows the registries included in the study, with data on work absenteeism, general practitioner (GP) consultations, pharmacy prescriptions, laboratory submissions, hospitalisations and mortality. Data were available for 1999–2009 or part of this period.

On the basis of available literature cited in PubMed on bioterrorism and natural infectious disease threats, we selected syndromes that were expected to reflect the clinical presentations of both high-threat (i.e. capable of causing major outbreaks of severe illness) and com-mon pathogens [16,17]. This not only makes it possible to use common pathogen activity as a test case for these syndromes, but also implies that emergence of the high-threat pathogens concerned will be relatively difficult to recognise by clinicians. We selected respi-ratory syndromes (e.g. for high-threat pathogens such as Bacillus anthracis or a new pandemic influenza vari-ant), gastroenteritis syndromes (e.g. caused by Vibrio cholerae infection) and neurological syndromes (e.g. caused by West Nile virus infection). The syndromes were defined for each registry, guided by a list of syn-drome definitions defined by the United States Centers for Disease Control and Prevention [18] and experts in infectious diseases and medical microbiology at the Rijksinstituut voor Volksgezondheid en Milieu (National Institute for Public Health and the Environment, RIVM). The syndromes were then evaluated per registry for their potential use in signalling infectious disease dynamics and outbreaks.

In this article, we present our perspective on the added value of syndromic surveillance for infectious disease surveillance and control, based on the results of our evaluation study and in light of the literature up to and including 2010.

Main findings of syndromic surveillance evaluation Tracking infectious disease dynamics in the general populationThe first question we addressed was to what extent trends in respiratory, gastroenteritis and neurologi-cal syndromes in the various registries reflect known pathogen activity, as measured by counts of detected pathogens (available from routine laboratory surveil-lance). This indicates whether these registries have the potential to reflect emerging pathogen activity (Table 2).

Of the three syndromes, respiratory syndromes were most closely associated with laboratory pathogen counts (Table 2), displaying higher levels in winter, which corresponded to higher counts of respiratory pathogens [19]. Up to 86% of the weekly syndrome var-iations (i.e. variance) in time were explained by weekly variations in respiratory pathogen counts, particularly

of influenza viruses and respiratory syncytial virus (RSV), which is in line with other studies [23,24]. However, the respiratory syndromes in our study were zero to five weeks ahead of laboratory counts of influ-enza viruses, suggesting better timeliness of these syndromes. For RSV, the pathogen counts were concur-rent with respiratory syndromes from hospitalisation registry data, which would be expected as most RSV tests are performed on hospitalised young children [25,26]. Most respiratory syndromes from other regis-try data lagged behind the RSV counts, which suggests that young children are affected relatively early in the annual RSV season.

The gastroenteritis syndromes showed winter peaks concurrent with increased rotavirus activity, and summer peaks concurrent with peaks in Shigella, Campylobacter and Salmonella activity (Table 2). Variation in the reporting of gastroenteritis syndromes explained by pathogen counts was lower (29–40%) than in the respiratory syndromes, although it increased up to 85% when limiting the analysis to young children, with the syndromes’ counts one to two weeks ahead of the laboratory rotavirus counts [20].

The reported general neurological syndromes did not clearly reflect known patterns of pathogen activity (Table 2). However, a more specific viral neurological syndrome – unexplained viral meningitis syndrome – in the hospitalisation registry data did: 62% of the var-iation in the reporting of this syndrome was explained by known seasonal enterovirus activity, suggesting that elevated levels of unexplained viral meningitis indicate undiagnosed enterovirus infections [22].

The general practitioner consultations, pharmacy pre-scriptions, hospitalisations and mortality registry data thus showed good performance in timely tracking of respiratory and/or gastrointestinal disease, and the hospital registry data also showed moderate perform-ance for neurological disease (Table 2). The advantage of using these four complementary registries together would be that they cover mild to very severe morbid-ity. The absenteeism registry data seemed most timely (ahead of laboratory surveillance data), but showed only moderate performance in tracking respiratory disease. This could be due to the fact that medical information is not available in this registry, and thus the data are a mix of all kinds of disease, although res-piratory disease is clearly reflected in the time-series pattern. The laboratory submissions registry data showed, at most, a moderate performance for the three syndromes evaluated.

Monitoring disease burden and detecting virulence shiftsThe second research question we addressed was whether syndromic surveillance improves the moni-toring of disease burden and detects shifts in the virulence of common pathogens. We evaluated this by relating time series of syndromic surveillance data with


pathogen-specific surveillance data to quantify the dis-ease burden due to common pathogens over time. We found a clear association over time of norovirus labo-ratory surveillance data with mild-to-severe morbidity and even deaths in elderly people, observed in recent years, coinciding with emergence of new norovirus var-iants [21]. The emergence of these variants had been suspected but could not be assessed by any other routine surveillance system. In addition, for influenza we detected previously unknown shifts in the annual numbers of hospitalisations and deaths related to the number of influenza-like illness (ILI) cases, coinciding with shifts in the antigenicity of circulating viruses [27]. Such analyses can also be used for investigating the severity of pandemic influenza A(H1N1)2009 infec-tion compared with that of seasonal influenza [28].

Detecting local outbreaksThe third question we addressed was whether syndro-mic surveillance can detect unexpected disease out-breaks in a timely manner. For this purpose, analysis of aggregated nationwide data may not be very sensitive: the large volume of the data (e.g. tens of thousands of respiratory syndrome hospitalisations per year) makes it impossible to detect outbreaks when they are still small. Local detection of syndrome elevations using a space–time algorithm might signal emerging out-breaks much sooner [29]. To test this, we used known outbreaks of Legionnaires’ disease as positive con-trols of realistic severe respiratory disease outbreaks due to uncommon or new pathogens that may not be detected by traditional surveillance in a timely man-ner. Simulating prospective surveillance, we were able to timely detect these known outbreaks in syndromic hospital data using space–time scan statistics [29]. The fact that the overall alarm rate was modest (a mean of five local clusters detected per year) suggests that syndromic surveillance of hospitalisation data for respiratory disease can indeed be a useful early-warn-ing tool for local outbreak detection. Using the same approach, previously unknown disease clusters plau-sibly due to Q fever were detected [30], thus illustrat-ing that on some occasions syndromic surveillance can identify outbreaks that otherwise would remain unde-tected. These analyses were motivated by the clinical detection of a large Q fever outbreak in 2007 and the subsequent years, which raised the question whether smaller outbreaks might have preceded the 2007 out-break. Real-time detection and investigation of these previously unknown clusters could possibly have led to earlier awareness of increased Q fever activity.

Assessing the absence or limited size of unusual disease eventsIn public health practice, besides timely detection of unusual outbreaks, being able to assess and commu-nicate the absence or limited size of unusual disease events can also be important. For example, Blendon et al. suggested that better communication to the pub-lic during the 2003 SARS outbreak might have pre-vented economic loss due to unnecessary precautions

taken by the public (e.g. many people stayed away from crowded places, even in areas with a relatively low level of spread of the virus) [31]. Also during high-profile public events (e.g. the Olympics or G8 summits) [32,33], syndromic surveillance will mainly confirm the absence of major, unusual disease outbreaks, since such outbreaks are rare events.

We also examined the value of syndromic data in assessing the absence or limited size of unusual dis-ease triggered by specific public health concerns. For West Nile virus (WNV) infection, enhanced surveil-lance was established in the Netherlands by labora-tory testing of cerebrospinal fluid (CSF) from patients with unexplained viral meningitis/encephalitis [22]. None of the CSFs collected in 2002 to 2004 tested positive for WNV, but the probability that WNV was indeed absent in the country could only be assessed from the annual count of unexplained viral meningitis/encephalitis cases (as a denominator in relation to the number of CSF samples tested). For hepatitis E and Ljungan virus infections, we inspected time series of unexplained hepatitis and abortion/perinatal death, respectively, and found no signs of emerging activity of these viruses. Rumours about a continuing increase of impetigo in children were countered by inspection of a time series of GP consultations for the infection.

Other spin-offs of syndromic surveillanceIn addition to the above described applications, other uses of syndromic surveillance were illustrated dur-ing the 2009 influenza A(H1N1) pandemic. We used respiratory syndromic data on hospitalisations and GP consultations to plan the diagnostic capacity that would be needed if a larger proportion of the persons with respiratory symptoms would be tested – as is the case in the early stages of a pandemic [34]. Also early in the pandemic, the reaction of the public to media reports on pandemic influenza was illustrated by sharp elevations in the number of oseltamivir prescriptions [35]. This information was used to urge physicians to exercise restraint in prescribing oseltamivir, in order to decrease the risk of oseltamivir shortage and viral resistance later in the pandemic.

Data requirementsThe results of our project suggest specific data require-ments for successful syndromic surveillance. Data quality is important for all applications of syndromic surveillance, but probably mostly for local outbreak detection. Here, relatively small artefacts – for exam-ple, duplicate details of the same patient in one reg-istry – can result in false alarms, as we experienced when using hospital data for space–time cluster detec-tion [29,30]. In a real-time setting (e.g. daily or weekly data updates), reporting delays can also lead to data artefacts and false alarms, if, for example, there is a delay in hospitals submitting their data [36]. In addi-tion to having few data artefacts, data need to be representative, and for local outbreak detection, they also need to have a high coverage (preferably close


to 100%) to be able to timely detect local outbreaks in any region. By using data with relatively low coverage levels, sensitivity for local outbreaks obviously will be reduced [37,38]. Nordin et al. used simulated anthrax attack data, and integrated the simulated data into actual physicians’ visit data to show that the sensitivity for detecting respiratory outbreaks resulting from bio-terrorism was not very high [37]. However, the authors evaluated a maximum system coverage of only 36% of the population. In another study, Balter et al. reported that a syndromic surveillance system in New York City sometimes missed several gastroenteritis outbreaks due to data quality (e.g. miscoding of patients’ chief complaints) and coverage problems (e.g. some hospi-tals did not participate in the system) [38].

For effective signal verification, sufficient information on individual patients’ characteristics and concurrent laboratory trends has to be available to identify possi-ble causes of generated signals. For example, we inter-preted local respiratory syndrome clusters in relation to local influenza or RSV activity: if the age distribution of cases reflected the usual pattern for these viruses, we regarded further investigation unnecessary [29]. Also, the rise in oseltamivir prescriptions early in the 2009 influenza A(H1N1) pandemic could be ascribed to the ‘worried well’, because laboratory surveillance showed that influenza virus activity had not increased [35]. Without such verification options, the value of syndromic surveillance is limited [38].

Cost-effectiveness of real-time surveillance systemsAn important question is whether syndromic surveil-lance is cost effective. Events such as a bioterrorist attack, a SARS epidemic or an influenza pandemic are rare and the question arises how much of the public health budget should be spent on a detection system for such rare events.

The costs of a surveillance system can be easily esti-mated. Studies that report the operating costs asso-ciated with real-time syndromic surveillance found annual operating costs ranging from US$ 130,000–150,000 to US$ 280,000 [39]. However, estimating its benefits is less obvious. Kaufmann et al. reported that the economic damage caused by a bioterrorist attack can amount to millions or even billions of dol-lars [40]. The SARS epidemic in 2003 and the influenza pandemic in 2009 showed that the economic damage caused by naturally occurring outbreaks can be simi-larly high [41,42]. If similar disease events emerge every few years, and syndromic surveillance leads to earlier detection and control of such outbreaks, then the benefits of syndromic surveillance are likely to outweigh its costs. The question here is whether ear-lier detection would indeed lead to control or at least reduced impact of a new disease, for instance, SARS or influenza A(H1N1)2009 infection. Simulation stud-ies could help to further evaluate which specific types of major disease events syndromic surveillance could

probably lead to interventions that limit the economic damage.

Possibly just as important as the benefits arising from earlier detection and control is the downscaling of unnecessary interventions during ongoing outbreaks. This requires quick assessment of the limited size and severity of outbreaks. For example, if the severity of a new pandemic can be quickly assessed – as the World Health Organization (WHO) requires [43] – by reliable syndromic hospital surveillance of severe respiratory infections, costly interventions such as quarantine and prophylactic treatment or vaccination could be downs-caled or stopped earlier if the disease is only mild.

In the Netherlands, prospective surveillance has now started for crude mortality data, with weekly data col-lection and analysis since the 2009 influenza pandemic. The existing mortality registry allows prospective implementation at relatively low extra cost. Real-time data collection is currently also being implemented for the Dutch GP registry (Table 1). Including hospital data and other data types in future syndromic surveillance systems may also be feasible at limited cost, if the data collection can be integrated into already planned real-time, future data infrastructures such as the Dutch national health-information-exchange system [44].

RecommendationsOn the basis of our evaluation, we recommend the use of syndromic surveillance to reveal blind spots of tradi-tional surveillance, in particular by detecting unusual, local outbreaks independently of laboratory diagnoses of specific pathogens, and by monitoring disease bur-den and virulence shifts of common pathogens.

Our results are mostly based on retrospective analysis of syndromic data of high quality and coverage. If pro-spective collection of such syndromic data is not feasi-ble, real-time early warning for local outbreaks should not be performed, since true outbreaks will probably be missed while at the same time numerous false alarms will be generated. For real-time early warning, sufficient laboratory and epidemiological information is needed, in order to be able to quickly verify possible causes of syndromic signals, and thus recognise rele-vant signals that might need a response. Retrospective analyses as performed in our evaluation can validate the relevant data and analyses before prospective implementation of a syndromic surveillance system.

AcknowledgementsWe thank Statistics Netherlands (CBS), the Dutch Foundation for Pharmaceutical Statistics (SFK), ISIS-labs, Dutch Hospital Data and Prismant (LMR), Netherlands Institute for Health Services Research (NIVEL) (regarding both the Netherlands Information Network of General Practice (LINH) and the Continuous Morbidity Registration (CMR) sentinel stations) for providing data, and the members of the Dutch Working Group on Clinical Virology, for providing access to the regis-try on weekly positive diagnostic results.


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